Dynamic sound reproducer



4 Sheets-Sheet l gvweutoz VES PER ANDERSON SCHLENKER y 7, 1934. v. A. SCHLENKER DYNAMIC SOUND REPRODUCER Filed. A ril 5, 1928 35 hm abhor/neg;

y 17, 4- v. A. SCHLENKER 1,966,564

DYNAMI G SOUN-D REPRODUCER Filed April 5,, 1928 4 Sheets-Sheet 2 vwwwoz VESPER ANDERSON SUMMER 331 his abhor/nu;

July 17, 1934. -v. A. SCHLENKER 1,966,564

DYNAMIC SOUND REPRODUCER FiledApril 5, 1928 4 Sheets-Sheet 3 'IIIIIIIIIIIlIIIllIlllI/IlflIIIIIIIIIIIIIIIIIIIA n u awuewto'c VESPER ANDERSON SCHLENKER 851 Wu abtowm y 1934- v. A. SCHLENKER 1,966,564

DYNAMIC SOUND REPRQDUCER I Filed April 5, 1928 4 Sheets-Sheet 4 avwenboz PER ANDERSON SEHLENKER 3313 kw) GHQ mug Patented July 17, 1934 f UJNiITEfD STATES? ere-TENT 1,966,564. .j DYNAMIC SOUND ni rnonuonn Vesper Anderson Schlenker,"Orange, N. J; Application April. 5, 1928, Serial No. 267,5

12 Claims. 7 (c1.'179--115;5)

This. invention relatesto sound reproducing apparatus for converting electrical currents into sounds corresponding thereto, and more especially to suchapparatus in whicha sound producing diaphragmis .Vibratedby the vibrations of an annularcoilt'mounted' for movement in an annular air gap;

ItfiS an object of this invention to provide a sound reproducer of. theclass described which 'rangements;

It is stilla further object of this invention, to provide a loud speaker in which the distortions heretofore inherent in" such. devices are elinri.--

nated: or substantially reduced while at the same time thepower: required for operation is alsoconsiderably reduced.

' It is still a further object of: this invention'to provide an. arrangement 'of'the movable coil which will permit a substantial reduction in the air gap necessary; thereby permitting a substantial reductionin the driving power utilized with.-

.' out sacrificingvolume or quality of reproduction.

. Still other objects and advantages of my invention will be apparent from the specification. The features of novelty which I believe to be characteristic of my invention-areset forth with particularity in the appended claims my inven tion itself, however, both as to its fundamental principles and as to. its particular applications will-bestbe understoodby reference to the specification and accompanying drawings, in which:

Figure 1 is a-crosssection of a. sound reproducer according to my inventiononlines 1,1.of Figure 4, I

Figure 2 is a detail sectionalview of the annular movable coil assembly showing the suspen- "1: sion removed. I V

I Figure 3 is aperspective View of the movable coil assembly showing the manner thereof.

Figure 4 is a front elevation of a sound reproducer according to my invention, partly broken away to show the construction thereof. Figure 5 is atop plan view of one of thes'uspension holders.

of suspension Figures 6, 7, and 8 are sectional views on lines- 1 .45; 7-7'and 8-8 of Figure 5 respectively:; and,

Figure 9 is an exploded sectional view showing the manner of assembly of the driving apparatus according tomy. invention,

v'Ihesound reproducer according to my invention comprises inits essentials, two elements,one being a new and improvedform of diaphragm. or I sound radiator, and the other being a new and improvedform of driving motor for vibrating the; sound radiator; The diaphragm or-sound radia tor-in itself, is shown and claimedinmy copending application, Serial Number 2 6 2,290, filed March 16, 1928, entitled Acoustic diaphragm", and; is capable of use with other formsoi driving motor: similarly, the: driving; motor shown, and claimed herein is capable of use with other forms of diaphragms or sound radiators in additionto that shown. However, I have found that par ticularly satisfactory. results are obtained by the,

use of. the, particular: sound radiator or; diaphragm hereinshown with the particular form of'dri-ving motor; g I

It has been suggested; in the past-,fpr-the purpose, of vibrating asound reproducingdiaphragm, I toutilize an annularcoi l. moyable in, an annular air gap, the telephonic currents. beingsupphed to the movable coil and a constant uni-directional magnetic flux being maintained, across the, annular: air gap. from an inner pole piece of one magnetic potentialto an outer pole piece of, the oppositev magnetic potential. In attempting to makeuse of such arrangementsfor drivingloud speakers adapted to be operated fromthe output of a broadcast radio receiver or electric pheno graph, considerations of: cost have so, far required the use or an. electro-magnet for establishing the fiux'in the air gap.;. While-it has been realized for-some timelthat aconsiderablesimplification of apparatus and decrease of cost would result if it were possible to utilize a permanent magnet for providing the magnetic flux throughthe an-.; nular-coil, this has so far not been practical because it hasbeen found impossible heretofore to utilize an air gapless than approximately .0 6"- in length, measured from; the inner pole piece to-the. corresponding point on the outer pole, piece With an air gap, of such magnitude, the permanent'magnet 'necessaryto establish a flux of sufli cient value for satisfactory operationwith the currents afiorded by the usual form of power tubes available-in the home; becomes of such size, weight and cost as praptically to render its use impossible. In 'the'past, it has not beenpractical; to reduce the sizeof the air gapbecause it was impossible to mount themovablecoil in; a manner which would permit or tre a ial mpveme t o the magnitudes desired, while preventing lateral motion of the coil or rocking in operation. This lateral motion or rocking results in the coil strik ing the inner or outer pole piece, particularly on swings of large amplitude, producing characteristic rattling noises and other undesired acoustic effects. 7 U

Moreover, even if the lateral motion or w'obbling referred to is not sufficient to cause the coil to strike against the pole piece, it serves to deform the diaphragm and to vibrate it in an undesired. manner, giving rise to over-emphasis of certain frequencies and partial suppression of others, and otherwise distorting the sound output.

In accordance with this invention, I provide a diaphragm which is in itself so arranged that distortions heretofore arising in the known types of diaphragms are eliminated or substantially reduced, and I provide a form of driving motor having an annular coil movable in an annular air gap of considerably smaller size than heretofore utilized.

I also mount or suspend the annular coil in a novel manner, as will be hereinafter pointed out more in detail, so that it is positively restricted to axial movement only and is not permitted to wobble laterally or rock in operation. As a result of such arrangements, I obtain a reproduction of sound of extreme purity and a sound wave which is an extremely faithful copy of the electrical currents supplied to the driving motor: moreover, since the size of the air gap is greatly reduced and since the losses resulting from the undesired motion of the drive are eliminated or substantially reduced, I obtain a considerably increased efficiency of'reproduction and am able to substantially reduce the power input necessary for a given sound output.

Referring now more particularly to Figure 1, 1 designates generally the core or frame of the magnet having an inner projection 2 terminating in the inner cylindrical pole face 2a. The magnet frame is also provided with an outer portion or skirt 3 in the form of a cup having a pair of outwardly extending flanges 3a and 3b (Fig. 4) enclosing the center pole piece 2, and which is of slightly less length than the center pole piece 2. The magnetic circuit is completed through the outer pole piece 4, having a circular aperture 5 surrounding the inner pole piece 2a and defining therewith a cylindrical air gap 5a within which the coil assembly 6 is mounted for axial movement. The surface of the skirt 3 engages the outer pole piece 4 and the corresponding surface of the pole piece 4, are preferably smoothly finished and pressed tightly together so as to minimize the magnetic reluctance of the joint, so that substantially the greater part of the drop in magnetic potential through the magnetic circuit comes within the annular air gap 5.

The annular coil assembly 6 comprises a cylindrical supporting member 8, preferably in the.

form of a sheet of conducting material, which is not quite closed in order to prevent or minimize its action as a short circuited turn. The form and position of the cylindrical member 8 is maintained by'a pair of end rings 9 and 10, the former of which comprises a cylindrical portion 11 and a circular portion 12, while the latter has a cylindrical portion 13 and a circular portion 14.. The end ring 9 is preferably directly in contact with the support 8 and is likewise cemented and soldered thereto, whereas the end ring 10 is separated from the support 8 by means of an insulated layer of silk or impregnated fabric 15 separating the member 3 and the cylindrical portion 13 of the end ring 10. The coil is wound up of the desired number of turns upon the cylindrical member 8 and will preferably be made in the form of a single layer of suitably insulated wire, one end of which is preferably soldered or otherwise grounded to the support 8: the other end is preferably soldered or otherwise connected to the end ring 10, whereby it will be observed that the end rings 9 and 10 serve as terminals for the annular coil. t will be observed that the longitudinal length of the coil '7 itself is substantially less than the coil assembly: preferably, the coil '7 is made about one third the length of the coil assembly and is positioned longitudinally in the center of the assembly for a purpose which will be described later. The end ring 9, it should be noted, is not put in position until the assembling of the apparatus, as will be hereafter described.

In order to prevent lateral displacement, wobbling or rocking of the coil assembly in operation, it is preferably suspended at each end by a direct acting and positive suspension, the front suspension assembly being designated as 20 and the rear suspension assembly as 21. Each of these suspensions comprises a pair of metallic ribbons disposed at an angle to each other and secured at the center to the coil assembly and at the outer ends to a support.

Referring now more particularly to Figure 3,- 2'2 and 23 designate the front suspension ribbons, and 24 and 25 the rear suspension ribbons. The outer ends of the ribbons 22 and 23 are'clamped between suspension blocks 26 and 2'7, while the 110 outer ends of the ribbons 24 and 25 are similarly clamped to the suspension blocks 28 and 29.

It is important that the suspension be arranged in a-manner to permit maximum vibration of the coil assembly 6 in operation, without stretching 115 the suspension ribbons beyond their elastic limit, and for this reason, the outer supports for the said ribbons are preferably made as far from the center of the coil as is practically possible, in order to provide a minimum change of length 120 as the coil moves in and out: also, I prefer to slightly crimp or corrugate the ribbons transversely or diagonally to their length before assembly, which serves to increase their apparent elasticity. The suspension ribbons are preferably made as thin as possible and relatively wide in order to provide for relatively heavy air damping on the ribbons themselves during the vibration of the coil, for the purpose of preventing the setting up of standing waves in the ribbons, and they are preferably assembled upon the suspension blocks under tension. As a result of this construction, it will be seen that a considerable resistance is interposed both as to lateral movement or wobbling of the coil in the air gap, 135 and also to rocking about its center, while the coil is left substantially free to vibrate axially.

It will also be observed with respect to this rocking movement, that if any rocking movement takes place about the center of the movable coil, it will be reduced in the ratio of two to one at the point on the coil in the air gap having the greatest amplitude of rocking motion, and still further reduced at interior points. With this construction I am able to utilize a clearance of only .006" between the coil assembly and the inner pole piece 2a, and only .008 between the coil assembly and the outer pole piece 4. Since the coilnassembly is only .Ole thick inthe air s heentire air gapmay; be no greater than ,030 in width. v Q v.F'orthe purpose of increasing the air damping onthe ribbons, order to prevent standin waves, I prefer to enclose or partially enclose. the ribbonsin a dead air chamber so as to obtain a dashrpot action. :This may be done-by forming the frontand rear suspension plates a and 3010 as shown in'Figures 5 W8 inclusive, in which it will be observed that these plates are provided with a circular-cut away opening 31 and aplurality of outwardly'extending legs. 32, 33,34 and 35, terminating in-flat portions 37, 38, 39 and 40, on which the clamping blocks are mounted. The outeredge 36 is preferably turned inward. so. as to'partially confine the air over a substantial portionof the length-of the ribbons. The center pole piece 2a'is preferably provided with slots and 46 through which' the lower suspension ribbons 24 and 25 pass: and'si'milar slots are also provided in the skirt portion 3 of the magnet. Also, damping may be had by as sociatingifelt, or wool, wi't'h the ribbons, or by securing paper or the like thereto. a In case it is desired to utilize an electro-magnetic field for driving the annular coil, an energizing winding 14 may be disposed in the space between *the inner pole piece 2 and the skirt 3, and for the purpose of facilitating the use of slightly fluctuating direct current in the winding 14, a relatively heavy ring of copper-14w may be placed onthetop thereof.- V

The diaphragm 48 is preferably constructed and-arranged in the manner'described in my copending application, SerialNumber 262,290,

filed March 16, 1928, entitled Acoustic diaphragm,-to which reference is had fora full and complete'understanding thereof; Forthe purposes ofthis application, I believe it suflicient to state that the diaphragm itself ispreferablyformed out of material having the least possible mass and dampingwithin itself, such for example as aluminum alloys, which have minimum mass andrelatively 'highstrength.

' The diaphragm is formed ofi'netal of-the great-f est possiblethinness, and preferably not" more than a fewthousandthsthick. satisfactoryre sultshave been obtained by the use of such alloys 0:002." thick' and having-a massnot exceeding' 0.03grams' per square'cen ti'meter.

The diaphragm is conveniently made in the axis which does not intersect" the'curve-withinl the generating segment, and the surface so produced will have the general shape of anex-- ponential horn. It is provided with a domed portion 49 at its center, which is reverselycurved, and the constants of the-generating curve, theaxisor revolution, and the segment used, are

so chosen 'thatsthe .slope of the diaphragmadjamaximum curvature in the radial direction 0c curs adjacent the outer edge of the diaphragm:

It will be'noted that under these conditions, the radial .curvature'is greatestv where-the circumtierentialcurvature issmallest, and vice 'mrsa.- .i .As a. result ofzthe'diaphragm construction just "'1 described, there .issobtainedra critically damped diaphragm having highcoupling-to the airaand relatively low. inherent damping. As a result of the structural stiffening given to the diaphragm by thereverse curvature-at right angles and as a result of other factors, flexural waves in-the material of such a diaphragm have a velocity of propagation which issubstantially. independent of frequency and approaches that-of speed of sound in air, and also the-attenuation of the diaphragm substantially independentof frequency, which operates to decrease phase and amplitude'distortion within the diaphragm. The diaphragm is attached to the coil assembly at, the circular .junction 50 between the domed portion 49' and an exterior portion of the diaphragm, and for the. purpose of providing anair seal to prevent air slippage around its periphery, it may be flexibly connected to a suit,- able baflie. board 52 provided with an inturned flange 53 by-means of an annulus or ring 51 of freely flexible and inelastic material, such, as leather, plush, or the like, which may'beglued to the periphery of the diaphragm and bentoyer the flange 53, and secured in position. by; one or more tension members such as string -.54. The particular air seal construction utilized forms per se no partof thisinvention.

;In assembling the apparatus thus far de scribed, the front and rear suspensionsarepreferably assembled independently, =the spacing blocks 27 and terminal blocks 61 beingpositioned upon the front suspension plate 30a on-theplane portions 3'7, 38, 39 and. 40, after which the ribbons 22 and .ZB are .placed in position'between the portions 37 and 39, and 38 and 40 respec-v tively. Thereafter, the clamping blocks 26 may be placed over the ribbons,- ,and clamping screws 62 and 63 inserted and drawn tight. ;In order to insure uniform tension and to avoid excesstension, the ribbons may be stretched to a pre-. determined tension by means of? spring balance or a weight, after which the clampingbolts may be tightened, and if .desired-a layerof'cement applied atthe joint. p After the front and rear suspensions 20 and 21 have been assembled, they will have the form shown in Figure 9; There'will-alsobe provided the outerpole piece 4 having theofiset end-portions 72 and 73' and provided with cut-away por-.-

tions 'ZOand '71. r

The apparatus may now be assembled as fol-.- lows: the. outer pole piece 4 may berplaced upon the magnet 1 and properly centered by'means of a suitable centering guage inserted. between the centerpole piece 20. and the outer pole piece; after which the outer pole piece-4 and the-flange portion 3a may be .suitably'drilled and dowel'led, the dowel pins being mounted in the polev piece 4.. The pole piece 4 will then be withdrawn:

4, its proper position heing determinedbyme'ans' of an outside centeringiguageor-clearance guage, positioned between the coilassembly and the outer pole piece 4. The-rear endring 10 will then.

be in contactwith the.rear suspension ribbons 24' andu25, and will :be soldered and cemented thereto. The outer centeringor-clearance guage may now. be removed; The front-suspension assembly will now be: attached to the outer-pole: piece. 4' and the magnet l returned'to the posi--' tion determinedby the dowel pins. previouslyv in.-:

serted. An inside centering guage will then be preferably inserted between the inner pole face 2a and the inside of the coil holder 8, and the magnet and coil assembly rigidly secured in position by bolts and nuts 83 and 84, after which the front end ring 9 will be positioned upon the coil support 8 and cemented and soldered in place, and thereafter the front suspension ribbons 22 and 23 may be cemented and soldered to the front end ring 9. Thereafter the offset portions '72 and '73 may be secured by means of screws 81 to the bafiieplate 52, to which the diaphragm has already been mounted and the diaphragm is cemented to the top end ring 9 at the circular edge 50. The leads supplying the telephonic currents may then be soldered to terminals 60 and 61.

While I have shown and described certain preferred embodiments of my invention, it will be understood that modifications and changes may be made without departing from the spirit and scope of my invention, and also, while I have referred to my apparatus as a sound reproducer, it'will be understood that it may also be used for the purpose of converting sound waves into 3 electrical currents.

1. In a sound reproducer, in combination, a magnethaving an inner pole piece and an outer pole piece surrounding said inner pole piece and defining an annular air gap, an annular coil movable in said air gap, and means for positively maintaining said coil against lateral displacement while permitting free axial movement of said coil, said means comprising a plurality of ten- 4. sioned ribbons in different planes secured to said coil and to an external support, and disposed at an angle to each other.

2. In a sound reproducer, in combination, a magnet having an inner pole piece and an outer pole piece surrounding said inner pole piece and defining an annular air gap, an annular coil movable in said air gap, and means for positively maintaining said coil against lateral displace-- ment while permitting free axial movement of said coil, said means comprising a plurality of tensioned metal ribbons in different planes secured to said coil and to an external support, the length of said ribbons being sufficiently great with respect to the amplitude of movement of .1 said coil so that the tension in said ribbons is at all times less than the elastic limit of the material of said ribbons, and said ribbons being disposed at an angle to each other.

3. In a sound reproducer, in combination, a

,; magnet having an inner pole piece and an outer pole piece surrounding said inner pole piece, and defining an annular air gap, an annular coil -movable in said air gap, and means for positively maintaining said coil against lateral displacement, while permitting free axial movement of said coil, said means comprising a plurality of metal ribbons secured to said coil and to an external support, and disposed at an angle to each other, the length of said ribbons being suiiiciently great with respect to the amplitude of movement of said coil so that the tension in said ribbons is at all times less than the elastic limit of the material of said ribbons, and said ribbons being moun ed in such manner that the damping thereon prevents the formation of waves in said ribbons during vibration of said coil.

4. In a sound reproducer, in combination, a magnet having an inner pole piece and an outer pole piece surrounding said inner pole piece, and defining an annular air gap, an annular coil movable in said air 'gap, and means for positively maintaining said coil against lateral displacement, while permitting free axial movement of said coil, said means comprising a plurality of tensioned metal ribbons in different planes secured to said coil and to an externalsupport, and disposed at an angle to each other, the length of said ribbons being sufiiciently great with respect to the amplitude .of movement of said coil so that the tension in said ribbons is always less than the elastic limit of the material of said ribbons, and said ribbons being crimped in such manner that the developed length thereof exceeds the actual length.

5. In a sound reproducer, in combination, a magnet having an inner pole piece and an outer pole piece surrounding saidinner pole piece, and defining an annular air gap, an annular coil movable in said air gap, and means for positively maintaining said coil against lateral dsplacement while permitting free axial movement of said coil, said means comprising a plurality of tensioned metal ribbons secured to said coil and to an external support at an angle to each other, the length of said ribbons being relatively great with respect to the amplitude of movement of said coil, and means for at least partially confining the air around said ribbons to suppress undesired vibrations thereof.

6. In a sound reproducer, in combination, a magnet having an inner pole piece and an outer pole piece surrounding said inner pole piece, and defining an annular air gap, an annular coil assembly movable in said air gap, and means for positively restricting said coil assembly to plunger action along its axis, comprising a front suspension mounted on the front side of said outer pole piece, and a rear suspension mounted on the rear side of said outer pole piece, each suspension comprising a plurality of tensioned ribbons disposed at an angle to each other, secured to said coil assembly and to an external support.

7. In a sound reproducer, in combination, a magnet having an inner pole piece and an outer pole piece surrounding said inner pole piece and defining an annular air gap, an annular coil assembly movable in said air gap, said assembly comprising a cylindrical form projecting out of said air gap at each end, and means for positively restricting said coil assembly to plunger action along its axis, said means comprising a front suspension mounted on the front side of said outer pole piece, and a rear suspension mounted on the rear side of said outer pole piece, eachsuspension comprising a plurality of tensioned ribbons disposed at an angle to each other secured to the projecting portion of said coil assembly, and to an external support, and the inner pole piece having openings therein through which the rear suspension ribbons pass.

8. Ina sound reproducer, in combination, a magnet having an inner pole piece and an outer pole piece surrounding said inner pole piece and defining an annular air gap, an annular coil assembly movable in said gap, said assembly comprising a winding support, and a winding mounted on said support, and an axially flexible conducting suspension at each end of said assembly, said suspensions forming the supply circuit to said coil.

9. In a sound'reprcducer, in combination, a magnet having an inner pole piece and an outer pole piece surrounding said inner'pole piece and defining'an annular air gap,an annular coil assembly ,movable in said gap, said assembly comprising a winding support, and a winding mounted on said support, an axially flexible suspension secured to said coil assembly, and a selfsupporting metallic diaphragm having curvature convex toward one side when out by a radial plane passing through the axis of the diaphragm and curvature concave toward the same side when cut by a plane perpendicular to said radial plane and spaced from said axis and having a mass not exceeding 0.03 grams per square centimeter secured to said coil assembly.

10. In a sound reproducer, in combination, a magnet having an inner pole piece and an outer pole piece surrounding said inner pole piece and defining an annular air gap, an annular coil assembly movable in said gap, said assembly comprising a winding support and a winding mounted on said support, an axially flexible suspension secured to said coil assembly at opposite ends and a self-supporting metallic diaphragm having reversed curvature in planes at right angles to each other and having a mass not exceeding 0.03 grams per square centimeter secured to said coil assembly.

11. In a sound reproducer, in combination, a

magnet having an inner pole piece and'an outer pole piece surrounding said inner pole piece and defining an annular air gap, an annular coil assembly movable in said gap, said assembly comprising a winding support and a winding mounted on said support, an axially flexible conducting suspension secured to said coil assembly at each end thereof for positively maintaining said coil against lateral displacement or rocking while permitting free axial movement thereof, and a. self supporting dynamically stable metallic diaphragm having a mass not exceeding 0.03 grams per square centimeter secured to said coil assembly.

12. A loudspeaker motor having a reciprocating armature and a support for the armature comprising at least two spaced spiders rigidly mounted at their outer portion and secured at their inner portion to the armature, said spiders being flexible in the direction of movement of the armature and rigid in the direction at right angles tothe direction of movement of the armature.

VESPER A. SCHLENKER. 

